1. Field of the Invention
Aspects of the present invention relate to a nonvolatile memory cell and a fabrication method thereof.
2. Description of the Related Art
Generally, nonvolatile memory devices may be classified as floating-gate memory devices and charge-trapping memory devices. Floating-gate memory devices are devices that maintain a charge by using a potential well. Charge-trapping memory devices are devices that trap charges in a trap region inside a nitride film, or in a trap region present in an interface between a nitride film and an insulator.
A representative form of a charge-trapping memory device is a Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) configuration. Typically, the SONOS configuration may include a sequential stack of a semiconductor substrate, an ONO configuration, and a gate electrode. The ONO configuration may include a sequential stack of a tunneling oxide film, a nitride film, and a blocking oxide film. The tunneling oxide film may tunnel electrons into a trap region inside the nitride film, or a trap region at an interface of the nitride film. The blocking oxide film may block charges from moving between the nitride film and the gate electrode. The trap region may store charges. Source/drain regions may be provided in the semiconductor substrate on either side of this stack.
Recently, the creation of a nonvolatile memory device on a glass substrate has been investigated. Such a configuration may include a sequential stack of the glass substrate, the ONO configuration, and the gate electrode. The glass substrate may include a protective layer, e.g., a buffer oxide film thereon, to protect the glass substrate. A polysilicon layer may be provided on the protective layer. Source/drain regions may be provided in the polysilicon layer on either side of this stack.
The creation of the polysilicon layer may include crystallizing an amorphous polysilicon layer, e.g., by irradiating the amorphous polysilicon layer with a laser. Thus, surfaces of the polysilicon layers may be rough and non-uniform, which may result in a large current leakage being generated. In other words, a current leakage may be significantly increased due to the non-uniformity and roughness of the surfaces of the polysilicon layer. Therefore, such a nonvolatile memory may function abnormally during storing/erasing operations